1. Field of the Invention
The present invention relates to a semiconductor fabricating method. More particularly, the present invention relates to a method of liquid crystal display (LCD).
2. Description of the Related Art
Since LCDs have advantages such as a low operating voltage, free of radiation scatter, light weight and small dimension, that the conventional cathode ray tubes (CRT) do not comprise. The LCD and other flat panel displays such as plasma display and electroluminance (EL) display, have thus become the main topic of the recent research on displays. These types of displays are also a leading trend for displays in 21st century.
LCDs substantially comprises a reflection type and a back-light type. Since the reflection-type LCD uses a reflection of an incident light source as the light for display without the application of a back-light source, the power consumption of the reflection-type LCD is lowered. In addition, the design of the reflection-type LCD is lighter and thinner in comparison with the back-light type LCD. Thus, the reflection-type LCD is widely applied in industry.
The substrate structure of the reflection-type LCD uses a metal layer having a smooth surface serving as a light reflection layer. The reflection layer acts as a mirror to reflect most of an incident light. However, as the incident light comes from the outside environment, the light intensity of this external light source is thus weaker than that of the back-light type LCD. Consequently, the displaying effect for the reflection type LCD is worse compared to the back-light type LCD. To optimize the displaying effect, it is often required the reflectance of the incident light source to be maximized.
To obtain an optimum reflectance, a passivation layer is typically formed on a device of the LCD to prevent erosion by moisture in the air and to avoid scratch by external mechanic force. This passivation layer has to be transparent. The structure and thickness of the passivation layer greatly affect the reflectance on a surface metal layer. Should the passivation layer be formed without proper care, an incident light may scatter randomly to reduce the intensity of the reflection, so as to degrade the quality of display.
FIG. 1 is a schematic, cross-sectional view showing a structure of a conventional passivation layer in a liquid crystal display.
In FIG. 1, a variety of devices (not shown) are formed on a substrate 100. An inter-metal dielectric (IMD) layer 110 is formed on the substrate 100. A patterned Ti/TiN layer 112 and a patterned top metal layer 114 are formed in sequence over the substrate 100. There are recesses and trenches, such as an opening 116, formed in the Ti/TiN layer 112 and the top metal layer 114. The opening 116 is formed in the patterned Ti/TiN layer 112 and the patterned top metal layer 114 to expose the inter-metal dielectric layer 110. A silicon oxide layer 120 and a silicon nitride layer 122 together serving as a passivation layer are formed in sequence over the substrate 100 to fill the opening 116.
However, the structure and the thickness of the above-described passivation layer have some drawbacks. In the conventional technique, the opening 116 is formed in the patterned top metal layer 114. The silicon oxide layer 120 and the silicon nitride layer 122 are formed along the opening 116. Thus, it is hard to obtain a planarized contour for the passivation layer. This, in turn, causes the scattering effect of the reflected light to become serious. The high reflectance of the top metal layer thus cannot be achieved.